1. Field of the Invention
The invention relates to the mining industry, and more specifically, it deals with a powered member.
The invention may be most advantageously used for stripping off large-size blocks of natural stone along a line of boreholes and for their subsequent splitting into blocks, for non-explosive driving of mining workings in rocks, or for demolishing foundations of old buildings and other structures. A powered member according to the invention when used in boreholes may find application for weakening difficult to break roof in working sheet deposits, for positive degassing of coal seams, fracturing oil and gas formations, for investigations into stress-strain state of a rock mass under field conditions and as a powerful small-size drive for actuator members of presses, jacks, guillotines and other devices where considerable directional forces should be developed.
2. Description of the Related Art
Hydraulic splitters are now widely used in the mining industry, and their construction has practically exhausted any possibility of further increase in a directive force developed by the splitters without an increase in weight and size.
In addition, the fact that the drive of a hydraulic splitter is located outside a borehole also results in an increase in weight of the hydraulic splitter because of the need to increase thickness of walls of the hydraulic splitter upon an increase in pressure in its hydraulic system.
The fact that a working member of the hydraulic splitter is disposed only in the mouth portion of a borehole substantially limits the field of application of hydraulic splitters and maximum splitting force as the directional propagation of a fracture is only possible in the immediate vicinity to the working member, and a concentration of load at the mouth of the borehole may cause surface spalling of a block rather than the formation of a predetermined splitting plane.
The provision of a radically new design of a powered member (SU, A, 1033829) has made it possible to achieve an increase in a directional splitting force.
Known in the art is a powered member having an axially parting casing accommodating a coaxially mounted flexible tubular chamber and a pair of spacer inserts each located on the casing parting line side. The insert is trapezoidal in section by a plane perpendicular with respect to the casing axis, the larger base of the trapezium bearing against the flexible chamber and the sides bearing against the inner wall of the casing. In addition, the powered member has a pair of rings, each having a nipple designed for supplying fluid to the interior of the flexible chamber. Each end of the flexible chamber is disposed between the nipple and ring. A perforated tubular core is provided to extend in the interior of the flexible chamber along the longitudinal axis thereof. Each end of the core is made in the form of a nipple. Each ring is in the form of a bushing having an inner thread coupled to an outer thread of the nipple. The rings are thus rigidly secured to each other by means of the tubular core. The rings are designed for sealing the ends of the flexible chamber.
When fluid under pressure is supplied to the interior space of the flexible chamber, the parts of the casing are tensioned under the action of both flexible chamber and spacer inserts. The prior art powered member is deficient in a low efficiency.
The efficiency here means the ratio of a force developed by the powered member in a predetermined direction to a force developed by the flexible chamber. For that reason the powered member has not found widespread use for splitting blocks of natural rock such as granite from the rock mass because of a limited force developed by the flexible chamber, e.g. 10 MPa. It is for this reason that the powered member could not develop the necessary force in a predetermined direction, i.e. perpendicularly with respect to the splitting plane. This is due to the fact that substantial axial loads developing in the tubular core cause its tension. This results in a clearance forming between the end face of the casing and the end face of each of the rings facing towards the flexible chamber. The material of the flexible chamber "flows out" into this clearance and is then broken. In addition, the tension of the core causes the loss of sealing of the ends of the flexible chamber which results in leakages of fluid. The elongation of the core may be reduced by increasing its cross-sectional area. This, however, results in a substantial increase in size and metal usage of the powered member or in a decrease in the workstroke of the movable parts of the casing and an increase in specific pressure at the point of engagement of the lateral faces of the inserts with the inner surface of the casing if the size remains unchanged which is undesirable because it would call for the employment of special materials and lubricants. It should be also noted that the trapezoidal configuration of the spacer inserts is not an optimum one because with a non-uniform pressure of the parting halves of the casing against the surface of the borehole a clearance is formed between the lateral face of each insert and the inner surface of the casing so that the material of the flexible chamber can "flow out" into this clearance.
The need to increase fluid pressure in the flexible tubular chamber to develope an increased directional splitting force resulted in the provision of a powered member disclosed in U.S. Pat. No. 4,690,460.
This prior art powered member comprises an axially parting casing accommodating a coaxially mounted tubular flexible chamber. The casing accommodates spacer inserts each located on the casing parting line side in a plane perpendicular with respect to the casing axis and having a trapezoidal cross-section with the larger base of the trapezium bearing against the flexible chamber and the sides bearing against the inner walls of the casing. A pair of nipples are provided for supplying fluid to the interior space of the flexible chamber and for air escape therefrom, which are located on the side of the end faces of the casing for movement along the longitudinal axis thereof, and a means for attaching each end of the flexible chamber to a head of the nipple. The means for attaching each end of the tubular flexible chamber to the nipple head comprises a bushing which is rigidly secured to a ring having a central passage for receiving the nipple which has its cylindrical portion conjugated with a conical portion having a generant inclined with respect to the longitudinal axis of the bushing at an angle corresponding to the angle of inclination of a conical surface of the nipple head, the generant of a conical surface of the ring being inclined with respect to the longitudinal axis of the ring at an angle corresponding to the angle of inclination of another conical surface of the nipple.
This construction of a powered member makes it possible to enlarge its field of application, e.g. for a non-explosive splitting of large-size blocks of hard natural stone, for fracturing boreholes in rock masses with the aim of evaluating the stress state of the earth crust, prevention of "rock shocks", and the like owing to an increase in maximum directional force developed by the powered member which is achieved by the casing of the powered member taking up the axial force which is the longitudinal component of fluid pressure in the flexible chamber. As the parting halves of the casing take up substantial axial forces during operation of the powered member, a prestressed design of the powered member is thereby provided. This rules out plastic deformation in the casing thereby enhancing reliability and prolonging life of the powered member. Reliability of the powered member in operation is enhanced owing to an increase in its axial rigidity with a substantial increase in fluid pressure in the flexible chamber since microclearances between the casing and flanges of the rings forming under high pressures become smaller. In addition, these microclearances are compensated for by the expansion of elastic members surrounding the tubular flexible chamber, each elastic member being received in an annular groove provided in the inner surface of the casing. Each elastic member engages the end face of the ring, surface of the annular groove and end face of the spacer insert. This rules out "flow-out" of the material of the flexible chamber into the spaces, hence, substantially enhances reliability of the powered member in operation with high fluid pressures in the flexible chamber which may be in excess of 100 MPa.
This construction of the powered member, is, however, characterized by a limited stroke of the parting halves of the casing so as to lower capacity of the powered member, reduce directiveness of the splitting force and increase the length of the powered member, hence its weight.